Bush has been in the hospital for a few days with low blood pressure and fatigue. In his tweet, he also noted that he was proud of the authors of the book, which was released June 1 and was written by two of his grandchildren — Ellie LaBlond Sosa and Kelly Anne Chase.

Sosa wrote on her Instagram account, “This is a love story – 77 years together, through the lowest lows and highest highs you can imagine and throughout it all, until the very end, their love was steadfast. What an example they have set for all of us! I hope you will love reading it as much as we loved researching and writing it.”

The former first lady passed away at 92 on April 17, leaving behind her husband, former President George H.W. Bush, the 41st U.S. president. Their marriage, which spanned 73 years, is filled with memorable moments.

They stood by each other’s side since they wed in January 1945, and had five children, including George W. Bush, the 43rd president, and Jeb Bush, the 43rd governor of Florida. The couple also had 14 grandchildren and seven great-grandchildren.

Barbara was the second lady of the U.S. from 1981 to 1989, and the first lady from 1989 to 1993. According to the Houston Chronicle, Barbara and George hold the record for the longest presidential marriage in U.S. history, surpassing John and Abigail Adams’s 54-year marriage. “I am still old and still in love with the man I married 72 years ago,” she told Smith College alumnae magazine.